OBJECTIVES: Macrophages of the reticuloendothelial system play an essential role in iron metabolism. Over 90% of iron utilized by the erythron is recycled from macrophage phagocytosis of senescent red cells with subsequent processing and release of heme iron to transferrin. Our objectives in this project are to 1) develop an in vitro assay of red cell iron release from human macrophages, 2) utilize this assay to examine: a) the kinetics, mechanisms, and control of macrophage iron release, b) the metabolic events required for macrophage iron release, and c) defects in macrophage iron release that may exist in the anemia of inflammation and idiopathic hemochromatosis. METHODS: Human monocyte monolayers will be prepared and allowed to develop into macrophages by greater than 14 days of in vitro culture. Mouse red cells will be labeled with 59Fe, opsonized with antibody and complement, and then added to human macrophage monolayers. 59Fe release from macrophages, into the supernates will be measured after fractionation into transferrin- and non-transferrin-59Fe.